Arc-type oscillators



Aug. 27, 1957 w. c. RUDD 2,804,562

ARC-TYPE OSCILLATORS Filed 001;. 20, 1954 2 Sheets-Sheet l Fig. 5

CARBON ARC WALLACE C. RUDD ATTORNEYS 1957 w. c. RUDD 2,804,562

ARC-TYPE OSCILLATORS INVENTOR. w}; WALLACE C. RUDD I dmd, fladlMwiSlmDmz8 momma ATTORNEYS 'best vacuum tube oscillator circuits.

ARC-TYPE QSQILLATORS Wallace C. Rudd, ,Larchrnont, N.'Y., assignor toMagnetic Heating Corp New Rochelle, N. Y., a corporation of New YorkApplication October 20, 1-954, Serial No. 463,351

4 Claims. (Cl. 313-447) This invention relates to oscillator circuitsfor generating "high frequency current and more particularly to improvedarc constructions adapted for use in such circuits.

In order to produce high frequency currentfor induction heating andother purposes and by using commercially available 60-cycle alternatingcurrent supplies as the source of power, ithas fora number of years beencornmon practice to use vacuum tube oscillators where frequencies of theorder of several hundred thousands of cycles are desired, or to usemotor-driven alternators Where frequencies of the order of ten or morethousand cycles per second are desired. The initial cost of equipment ofeither type, and particularly the latter, is, however, relatively largeand under some conditions the maintainence costs are excessive. Manyyears ago an arc-type oscillator was developed by Valdimar Poulsen,which was used to some extent for producing high frequency currents forradio purposes, his circuit being'a modification of the Dudell MusicalArc circuit. While such arc-type oscillators were relatively simple andinexpensive, they embodied various-recognized shortcomings, such thatthey were substantially superseded by vacuum tube type oscillators ofgreater reliability.

The general purpose of the present invention, however, is to providesuch an improved form of arc construction for the Poulsen typeoscillator circuit as to insure reliable operation with the initial costand maintenance costs substantially below those of other types ofoscillators and yet having an efficiency comparable to that of the Thehigh frequency generators of the present invention are well adapted foruse-with an ordinary 60-cycle commercial current source of 449 volts forexample, to produce high frequency of the order of 10,900 cycles orhigher with an output in the neighborhood of 20 kilowatts or more. Theseresults have been accomplished by making a number of improvements in theconstruction and operation of the Poulsen type are, as willbe-hereinafter described. Such improvements have resulted in a veryreliable high frequency generator having an efficiency in theneighborhood of 5 50%, which is comparable to that of present-dayinduction heating equipment so far as concerns typical operatingcharacteristics, but with the addition of greater simplicity andcheapness of construction.

Other and more specific objects, features, and advantages of theinvention will appear from the detailed description given below, takenin connection with the accompanying drawings forming a part of thisspecification and illustrating by way of example the presently preferredembodiment of the invention.

In the drawings:

Figure l is a diagrammatic view of a conventional circuit of the Poulsentype oscillator as adapted for an alternating current source of supply;

Figure 2 is a vertical sectional View showing the improved arcconstruction according to a preferred embodimenLof the invention;

States Patent 2,804,562 Patented Aug. 27, 1957 Figure 3 is a somewhatschematic transverse vertical sectional view of a portion of theapparatus of Fig. 2;

Figure 4 is a diagram illustratinga means'for maintaining an atmosphereor hydrogen or other gas in the arc chamber; and t Figure 5 is asectional view illustrating more fully-one of the electrode stop meanshereinafter described.

The conventional circuit, as shown in Fig. 1, comprises an arc withcarbon electrodes-as indicated, supplied from a source of low frequencyalternating current through a reactance with a laminated iron core asindicated at R. In parallel with the arc electrodes, a capacitor Cand'an inductance I are connected in series. When the arcis struck bybringing the electrodes together and then-sen arating same, a negativeresistance characteristic is produced. This negative resistancecharacteristic (according to which the greater the current, the lowerthe voltage drop across the arc) causes such circuit to operate as anoscillator to produce high frequency alternating current in thecapacitor-inductance circuit. Since high frequency current flows in thiscircuit, it may be conveniently used for induction heating, and variousother purposes, for example by placing the object to be heated insidethe inductance I, such inductance in this case being the work coil, orof course such circuit may be used by making the inductance I theprimary of a high frequency transformer, the secondary of which feeds aconventional work coil and load combination.

Poulsen improved the Dudell musical arc circuit by installing a directcurrent magnetic field at right angles to the arc electrodes which werefed with direct current. Such magnetic field caused the arc to be blownover to one side of the electrodes and to remain at a predeterminedposition. With the Poulsen construction, the electrodes were constructedrespectively of a carbon rod and a water-cooled copper block, each withits own direct current polarity. The carbon rod was rotated andautomatically advanced axially in order to compensate for the carbonconsumption during the operation.

For a variety of reasons, I have found that high frequency current ismost efiiciently produced with this circuit if carbon or graphiteelectrodes are used and if the arc is maintained in an atmosphere ofhydrogen, or one containing considerable hydrogen. However, anatmosphere of other gases such as illuminating gas may be used, but acarbon deposit will then be created on the inside of the gas chamberwhich would require periodic cleaning. if the arc chamber is filled withair, only a very small amount of high frequency current is produced, butif hydrogen or some other gas or vapor containing hydrogen is used, theproduction of high frequency current is made possible with a quitesatisfactory efiiciency.

Since for widespread present-day use, such equipment should be designedfor use with an alternating current source of supply, the Poulsen copperelectrode is eliminated and carbon or graphite is used for bothelectrodes according to the present invention. An to insure uniformburning of the carbon, the Poulsen arc magnetic field is used, but inthe form of an alternating current field, and preferably the reactance Rof the supply circuit is used to supply such a field to blow the areinto a stable position at one side of the electrodes while theelectrodes are being rotated, preferably relatively rotated andpreferably, but not necessarily, in opposite directions.

However, with the arrangement as thus far described there would remaintwo problems which so far as known have not heretofore beensatisfactorily solved in any simple, practical and depend-able way, viz.first the arc would be irregular and variable in length because of thedifficulties of axially feeding the electrodes .at the proper ratetoward each other to insure an arc of constant length as the carbon orgraphite becomes burned away, and secondly with the are blown to theperipheries of the ends of the electrodes, such peripheries would becomeburned away more rapidly than the central portions so that the centralportions, when fed toward each other, would either come into contactland eliminate the arc or provide a shorter path causing irregularitiesin the arc. Efforts to avoid these difficulties were made with a varietyof electrode arrangements such as with electrodes at various angularrelationships or with one electrode offset with respect to the other orconcentric with the other, but by far the most satisfactory arrangementwas found to be with the electrodes in spaced end-to-eud alignment andwith each electrode formed with a hollowed-out center, the centralcavities being sulficinetly large so that the arc, as the electrodes areoppositely rotated, will uniformly burn away all of the carbon, sincethe carbon is located only at the peripheral portions at the end of eachelectrode. While the construction of the electrodes in hollowcylindrical form with means to uniformly and relatively rotate sameabout their axes, insures against creation of any grooves or irregularunburned areas at the ends of the electrodes, still this leaves no wayin which to predict the rate (which may sometimes vary) at which theelectrodes should be fed toward each other. And since the electrodes areto be contained within a gas-filled chamber, it is difiicult todetermine visually whether or not they are being fed at the properspeed. However, according to the present invention, this problem issolved by using the ends of the electrodes in the are chamber as theactual reference points for determining the rate of feeding. This isaccomplished by arranging two insulated water-cooled spacers or stopmeans located in contact with the facing ends respectively of theelectrodes, while each of the electrodes are separately urged by springmeans or otherwise, constantly into contact with the respective stopmeans. In this way, the electrode spacing is satisfactorily maintainedat a constant value.

With the above considerations in mind, the construction of Fig. 2 willnow be described. The two carbon or graphite hollow cylindricalelectrodes are indicated at and 11 respectively, positioned in spacedend-to-end aligned relation within a gas chamber 12 formed of copper orbrass, for example. This chamber may be protected from overheating as byapplication of circulating cooling fluid conduits as at 13 on theexterior thereof. The electrodes protrude into the chamber respectivelythrough openings 14, 15, and outside the chamber portions of theelectrodes are surrounded by insulation cylinders at at 16, 17 formed ofquartz, for example, and protected against overheating as by coilscontaining cooling fluid as indicated at 18 and i9 surrounding metalflanges 2t 21 formed about the chamber openings 14 and 15. The outerends of the insulation cylinders 16, 17 may be closed as by metal plates22, 23 suitably apertured to receive the electrodes and carrying copperor brass bearing members as at 24, 25, within which the electrodes mayrotate.

The outer ends of the electrodes respectively may be covered by brass orcopper cap members as at 26, 27, upon which sprockets as at 28, 29 aremounted in position to be driven from motors 30, 31 respectively throughbelt or chain means as shown at 32, 33.

Each of the cap members 25, 2'! and thus also the electrodes, areconstantly urged inwardly of the are chamber by helical springs 34, 35respectively, which may bear against frame means as at 36, 37. Theplates or frame parts 22, 36 and 23, 37 may be secured together as byrods 38 and the frame means at one end of assembly may be clamped orsupported by a suitable insulation clamping means or the like (notshown) with respect to the frame means at the other end of the assemblyand so as to hold the quartz cylinders 16 and 17 4 in the positionsshown. The two electrical terminal connections for the source of powermay be applied to the rods 38 and as indicated at 40, 41.

The stop means, such as above referred to, are indicated at 42, 43 forengaging the facing ends of the electrodes as pushed toward each otherby the springs 34, 35. These stop means may comprise angularly shapedblocks of copper or brass as shown supported upon pairs of tubes as at42, 43' which form conduits for streams of cooling fluid to preventoverheating of the stops.

As best shown in Fig. 3, the stop means 4-2, 43 may preferably belocated at positions Spaced angularly apart about the electrodes byabout 120 and at the same time they will then each be located atpositions spaced also about 120 from the normal position of the are, asindicated at 45, assuming that the source of the magnetic field forblowing the are into this position is located below the chamber.Preferably as above indicated, the source of the magnetic fieldcomprises the iron core re actance R above referred to in connectionwith the circuit of Fig. l.

The cooling fluid conduits which support the stops 42, 43 may, as shown,extend through suitable insulation supporting means as at 46, 47 mountedon the walls of the arc chamber.

Various known means for starting the arc may be used, but in the formshown in Figs. 2 and 3, a wedge-shaped piece of carbon 48 is mountedupon a suitable inwardly slidable insulation rod 49. Thus after thecurrent source is connected to the terminals 4t 41 as per the circuit ofFig. l, the carbon wedge 4% is momentarily thrust i11- wardly of the arcchamber to the position shown at 48 in Fig. 2 and then withdrawn,leaving established a single are between the ends of the electrodes 19and 11. And if the reactance R is positioned as shown, the alternatingfield maintained thereby will act to retain the arc in the upperposition as shown in Fig. 3. Since the current flowing through the arcis alternating (from a -cycle source, for example), it will beappreciated that the electromagnetic field used to retain the arc inthis position should also be alternating and in phase with thealternating arc current, but of course this is assured by using thereactance R of the power supply source for the double purpose ofestablishing the field for controlling the arc and for properly limitingthe supply of alternating current to the oscillating circuit.

Before the arc is started, the chamber 12 should be purged of air andthe air replaced by the desired gaseous atmospher, such as hydrogen. Andsince there maybe some slow leakage of gas from the arc chamber, thechamber is preferably constantly supplied with gas in the manner shownin Fig. 4. Here a small constant supply of hydrogen is provided througha conduit 52 which extends down to near the bottom of a chamber 53containing a small volume of liquid 54 such as mercury. The gas thus isallowed to bubble up through the mercury and from the chamber 53 intothe arc chamber through a conduit 55. Gas may constantly be withdrawn insmall quantities from the arc chamber through a conduit 56 which extendsdown close to the bottom of another chamber 57, also containing a bodyof liquid 58, such as mercury, through which the discharged gas bubblesup and finally escapes to a desired discharge point through a conduit59. in this way an atmosphere of the desired gas may be readilymaintained at a substantially constant pressure above atmosphericpressure in the arc chamber and acting to exclude any possibility ofleakage of air into the arc chamber.

The specific example of the apparatus above described was designed tooperate from a source of 60-cycle current supply at 446 volts to providea high frequency generator having an output of 20 kilowatts at afrequency of about 10,000 cycles per second, the 60-cycle alternatingcurrent being translated into high frequency current with an efficiencyof about 50%. This was accomplished by using a current of about 100amperes (when having unity power factor). With this particular exampleof the apparatus, it was found that the most desirable operatingcharacteristics were obtained when the capacity C was about 11.2microfarads and when the inductance I had a value of about 25microhenries. These factors will, of course, vary depending upon theparticular design of the apparatus, the particular high frequencydesired and other characteristics thereof, but although such factors arefairly critical, for best results the values thereof may readily bedetermined by trial. With the particular installation as described, thevalue of the reactance R was 6.4 millihenries, The electrodes and 11 hadan outside diameter of about 2 inches and a quarter inch wall thickness.When the motors 30, 31 rotates such electrodes in opposite directions ata speed in the neighborhood of three revolutions per minute, theelectrode walls were consumed by the arc gradually and completely assame were advanced by the springs 34, 35 and held in contact with thestops 42, 43, respectively. The space between electrodes may be of theorder of A to A".

While the electrodes may be conveniently and preferably rotated inopposite directions to insure uniform consumption thereof at all pointsaround their end edges, yet satisfactory results may be obtained byrotating them both in the same direction but at somewhat differentspeeds. Since the arc is held in a stationary position by the magneticfield, it will have opportunity to come into contact successively withall points on the end edges of the electrodes if the electrodes arerotated about their axes and whether or not they are rotated atdifferent speeds or in opposite directions. But by relatively rotatingthem, irregularities in the burning tend to be more safely avoided androtation thereof in opposite directions at the same speed will generallybe most convenient.

Although one particular embodiment of the invention is here disclosedfor purposes of explanation, various modifications thereof, after studyof this specification, will be apparent to those skilled in the art towhich the invention pertains. Reference should accordingly be had to theappended claims in determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. An arc construction adapted for use in an oscillator circuit andcomprising a pair of hollow cylindrical electrodes formed of carbonmaterial, means for supporting said electrodes substantially in endwisealignment with an arc gap between the ends thereof, means for relativelyrotating same about their axes, fluid cooled stops for engaging portionson the facing ends thereof respectively to maintain the gap therebetweenof predetermined length, means for normally constantly urging each ofsaid electrodes against said stops respectively, means for maintaining amagnetic field in said gap with lines of force running transversely ofthe electrodes to cause an are between the electrode ends to assume aposition spaced from said stops, a chamber for enclosing the region ofthe arc, and means for maintaining a hydrogen-containing atmospherenormally above atmospheric pressure in said chamber.

2. An arc construction comprising a pair of electrodes formed of carbonmaterial and having annular ends, means for supporting said electrodessubstantially in endwise alignment with an arc gap between said annularends, means for rotating said electrodes about their axes, stops forengaging said annular ends respectively to maintain the gap therebetweenof predetermined length, means for maintaining said ends as they burnaway in contact with said stops respectively, and means for maintaininga magnetic field in said gap to cause the arc to assume a predeterminedposition between said annular ends.

3. In an arc construction, a pair of electrodes formed of carbonmaterial, means for supporting said electrodes substantially in endwisealigmnent with an arc gap between the ends thereof, means for relativelyrotating same about their axes, and means for maintaining a magneticfield in said gap with lines of force running transversely of theelectrodes to cause an arc therebetween to be blown to one side of thegap and confined to the peripheries of the electrodes, the said endportions at least of said electrodes being hollowed out to an extentwhereby the whole end surfaces will be burned away by the arc.

4. An arc construction comprising a pair of hollowended electrodesformed of carbon material, means for supporting said electrodes with anarc gap between such ends, means for rotating same about their axes,stops for engaging portions on the facing ends thereof respectively tomaintain the gap therebetween of predetermined length, means formaintaining said electrodes with their ends as they burn away in contactwith said stops respectively, and means for maintaining a magnetic fieldin said gap with lines of force running transversely of the electrodesto cause the arc between the electrodes to assume a substantially stableposition spaced from said stops.

References Cited in the file of this patent UNITED STATES PATENTS1,906,491 Spieth May 2, 1933 2,449,552 Gorham Sept. 21, 1948 2,450,477Huff Oct. 5, 1948 2,456,902 Treuthart Dec. 21, 1948

